1. Field of the Invention
This invention relates generally to a spinal implant assembly for implantation into the intervertebral space between adjacent vertebral bones to potentiate fusion, and more particularly to a coupling member which is attachable to laterally offset intervertebral cage devices to prevent rolling thereof and to enhance the lateral stability and overall strength thereof
2. Description of the Prior Art
The bones and connective tissue of an adult human spinal column consists of more than 20 discrete bones coupled sequentially to one another by a tri-joint complex which consists of an anterior disc and the two posterior facet joints, the anterior discs of adjacent bones being cushioned by cartilage spacers referred to as intervertebral discs. These more than 20 bones are anatomically categorized as being members of one of four classifications: cervical, thoracic, lumbar, or sacral. The cervical portion of the spine, which comprises the top of the spine, up to the base of the skull, includes the first 7 vertebrae. The intermediate 12 bones are the thoracic vertebrae, and connect to the lower spine comprising the 5 lumbar vertebrae. The base of the spine is the sacral bones (including the coccyx). The component bones of the cervical spine are generally smaller than those of the thoracic spine, which are in turn smaller than those of the lumbar region. The sacral region connects laterally to the pelvis. While the sacral region is an integral part of the spine, for the purposes of fusion surgeries and for this disclosure, the word spine shall refer only to the cervical, thoracic, and lumbar regions.
The spinal column of bones is highly complex in that it includes over twenty bones coupled to one another, housing and protecting critical elements of the nervous system having innumerable peripheral nerves and circulatory bodies in close proximity. In spite of these complications, the spine is a highly flexible structure, capable of a high degree of curvature and twist in nearly every direction.
Genetic or developmental irregularities, trauma, chronic stress, tumors, and degenerative wear are a few of the causes which can result in spinal pathologies for which surgical intervention may be necessary. A variety of systems have been disclosed in the art which achieve immobilization and/or fusion of adjacent bones by implanting artificial assemblies in or on the spinal column. The region of the back which needs to be immobilized, as well as the individual variations in anatomy, determine the appropriate surgical protocol and implantation assembly. With respect to the failure of the intervertebral disc, the interbody fusion cage has generated substantial interest because it can be implanted laparoscopically into the anterior of the spine, thus reducing operating room time, patient recovery time, and scarification.
Referring now to FIGS. 1 and 2, in which a perspective view of an intervertebral body cage 10 and a perspective view of an intervertebral spacer device 50 are shown, respectively, a more complete description of these devices of the prior art is herein provided. The cage device 10 generally comprises a tubular metal body 12 having an external surface threading 14. Pairs of these devices are inserted transverse to the axis of the spine, into preformed cylindrical holes at the junction of adjacent vertebral bodies. Two cages 10 are generally inserted side by side with the external threading 14 tapping into the lower surface of the vertebral bone above, and the upper surface of the vertebral bone below. The cages 10 include holes 18 through which the adjacent bones are to grow. Additional material, for example autogenous bone graft materials, may be inserted into the hollow interior 20 of the cage 10 to incite or accelerate the growth of the bone into the cage. End caps (not shown) are often utilized to hold the bone graft material within the cage 10. Intervertebral spacer devices 50 of the type shown in FIG. 2 are similarly positioned, between adjacent vertebral bones, however, they may be solid or hollow, and provide a greater volume of bone graft material to be placed between the two devices 50. More specifically, these intervertebral spacer devices include a solid body 52 having a flat top surface 54 and a flat bottom surface 56. The top and bottom surfaces include serrated ridges 58 which are aligned perpendicular to the axis of the body 52. The sides 60 of the body 52 are concave so that pairs of these devices, when placed side by side, can receive bone graft material between them, thus enhancing the process of bone fusion across the adjacent vertebral bodies.
These cages and intervertebral spacers of the prior art have enjoyed medical success in promoting fusion and grossly approximating proper disc height, however, they do have specific concers regarding their effectiveness. Chief among these concerns is that there will be a tendency for the devices to roll and/or slide. Such undesirable motion by the implant can cause loosening, or worse, complete dislocation from their proper position.
It is, therefore, an object of the present invention to provide an implant which further enhances the stability of cage and/or intervertebral stabilization devices.
It is a further object of the present invention to minimize the risk of dislocation by providing a device which prevents rotational and lateral movement of cage and/or intervertebral stabilization devices.
Other objects of the present invention not explicitly stated will be set forth and will be more clearly understood in conjunction with the descriptions of the preferred embodiments disclosed hereafter.